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2.2.2 Thermistor(MCP3008)

Nota

Depending on your kit version, please identify whether you have ADC0834 or MCP3008 and proceed with the matching section.

Introduction

Just like photoresistor can sense light, thermistor is a temperature sensitive electronic device that can be used for realizing functions of temperature control, such as making a heat alarm.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
Placa de Extensión GPIO	COMPRAR
Protoboard	COMPRAR
Cables de Puente	COMPRAR
Resistor	COMPRAR
Termistor	COMPRAR
MCP3008	-

Schematic Diagram

T-Board Name	physical	WiringPi	BCM
SPICE0	pin24	10	8
SPIMOSI	pin19	12	10
SPIMISO	pin21	13	9
SPISCLK	pin23	14	11

Experimental Procedures

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

cd ~/raphael-kit/nodejs/

Step 3: Run the code.

sudo node thermistor-2.js

With the code run, the thermistor detects ambient temperature which will be printed on the screen once it finishes the program calculation.

Code

const mcpadc = require('mcp-spi-adc');

// Open MCP3008 channel 0 (CH0), analog input from thermistor voltage divider
const adc = mcpadc.openMcp3008(0, { speedHz: 1350000 }, (err) => {
  if (err) {
    console.error('Failed to open MCP3008 channel:', err);
    process.exit(1);
  }

  console.log('MCP3008 thermistor channel opened.');

  setInterval(() => {
    adc.read((err, reading) => {
      if (err) {
        console.error('ADC read error:', err);
        return;
      }

      const adcValue = reading.value; // Float: 0.0–1.0
      const raw = Math.round(adcValue * 1023); // 10-bit integer value

      const Vr = 3.3 * raw / 1023; // Convert to voltage (assuming 3.3V Vref)
      const R0 = 10000;            // Fixed resistor: 10k
      const B = 3950;              // B constant
      const Rt = R0 * Vr / (3.3 - Vr); // Thermistor resistance

      const tempK = 1 / ((Math.log(Rt / R0) / B) + (1 / (273.15 + 25))); // Kelvin
      const tempC = tempK - 273.15; // Celsius
      const tempF = tempC * 1.8 + 32; // Fahrenheit

      console.log(`Celsius: ${tempC.toFixed(2)} °C  |  Fahrenheit: ${tempF.toFixed(2)} °F`);
    });
  }, 1000);
});

Code Explanation

setInterval(() => {
  adc.read((err, reading) => {
    ...
  });
}, 1000);

Sets up a loop to read from MCP3008 channel 0 every 1000 milliseconds (1 second). The read function returns an analog value between 0.0 and 1.0.

const raw = Math.round(reading.value * 1023);

Converts the normalized float ADC value into a raw 10-bit integer (range 0–1023).

const Vr = 3.3 * raw / 1023;

Calculates the voltage at the thermistor (Vr) using the ADC reading. Assumes MCP3008 reference voltage is 3.3V.

const Rt = R0 * Vr / (3.3 - Vr);

Uses the voltage divider formula to calculate the thermistor resistance Rt, where R0 is a fixed resistor (10kΩ) in series.

const tempK = 1 / ((Math.log(Rt / R0) / B) + (1 / (273.15 + 25)));

This applies the B-parameter equation (a simplified form of the Steinhart-Hart equation) to estimate the temperature in Kelvin.

const tempC = tempK - 273.15;
const tempF = tempC * 1.8 + 32;

These convert the Kelvin temperature to Celsius and then Fahrenheit.

console.log(`Celsius: ${tempC.toFixed(2)} °C  |  Fahrenheit: ${tempF.toFixed(2)} °F`);

Prints both the Celsius and Fahrenheit temperature values with two decimal points of precision to the console.